The use of swearwords has hardly been investigated scientifically. Virtually nothing is known about the efficacy of swearing. The present studies set out to investigate whether the inclusion of swearwords in a testimony increases the believability of that statement. In study 1, respondents were simply asked whether they believed that using swearwords is a sign of credibility, a sign of deceit, or neither. In the second and third study, participants had to read fictitious testimonies of a suspect and a victim, respectively. Participants were exposed to testimonies with or without swearwords. The results suggested that people self-reported to find swearwords a sign of deceit (study 1), but when actually confronted with a statement, the opposite turned out to be the case (studies 2 and 3). That is, testimonies containing swearwords were perceived as more credible than swearword-free testimonies. Hence it is concluded that swearing increases believability of statements.